Most mobile machines include an operator cabin having a controlled environment that increases operator comfort. For example, the operator cabin can be heated, air conditioned, and or ventilated to maintain the operator cabin at a desired temperature. High-pressure air conditioning is a well known mechanism for cooling an enclosed space. However, conventional high-pressure air conditioners are bulky and inconvenient for mobile applications. Conventional air conditioners are also large and difficult to install. Resistive heating elements are also well known mechanisms and are commonly used for heating mobile machine cabins. While resistive heating elements do not generally suffer from space constraints, they are relatively inefficient at converting electrical energy into heat energy.
Some manufacturers of mobile machines have attempted to overcome the deficiencies of air conditioners and resistive heating elements by utilizing air-to-air heat pumps. In air-to-air heat pumps, heat is absorbed in an evaporator at a first location and released in a condenser at a second location. These systems are reversible so that the cabin of the machine may either be cooled or heated by the same system. In heating applications, air-to-air heat pump systems can be up to 300% efficient. Unfortunately, air-to-air heat pumps can also be expensive to maintain. Components of a heat pump are also relatively expensive, require expensive coolant, and need frequent maintenance.
An alternative system for cooling and heating a locomotive cabin is described in U.S. Pat. No. 5,628,203 (“the '203 patent”) of Adolph that issued on May 13, 1997. The '203 patent describes a locomotive having a heat exchanger, a turbine, and a compressor, all used to heat and cool the locomotive cabin. In a cooling operation, outside air is expanded in the turbine, cooled below ambient temperature, and introduced into the heat exchanger. Hot air from the cabin is simultaneously introduced into the heat exchanger, where heat transfers from the hot cabin air to the cool outside air. The cooled cabin air is then directed to the cabin and heated outside air is expelled to the atmosphere. In a heating operation, a valve establishes fluid communication between the heat exchanger and the compressor. Cold air from the turbine is heated by air from the cabin, is further heated by the compressor, and is directed into the cabin, resulting in a net heating effect of the cabin.
Although the system of the '203 patent may be capable of heating and cooling a locomotive cab without resistive heating elements or a conventional air conditioner, it may still be less than optimal. Specifically, because the system of the '203 patent utilizes ambient air as a coolant and heat source, the system may suffer from a relatively low coefficient of performance.
The HVAC system of the present disclosure solve one or more of the problems set forth above and/or other problems with existing technologies.